An acrylamide-agarose composite gel electrophoresis method has been developed to separate the different species of RNA and ribosomes from mouse liver and HeLa cells. The polyribosomes can readily be separated into their components, from monosomes to hexamers. A method to study the type of RNA in the ribosomes has also been successfully developed by using a second dimension electrophoresis. This method is being used to study in vivo binding of 14C-dimethylnitrosamine (DMN) to rRNA. DMN was found to cause dissaggregation of polyribosomes.